[evlatests] PDif compression -- more tests

[Rick Perley]

    Not that I can recall.  But ... this mechanism would affect the 
old-style X-band receivers equally as the new.  Yet we have clear 
evidence the old-style (VLA) receivers showed very little compression, 
while the new ones are as affected as the other bands ...

    But a test should be done. 

Ken Sowinski wrote:
> On Tue, 5 Mar 2013, Rick Perley wrote:
>
>>    Result:  No change in PDif compression.  These three antennas are
>> still as bad as they were before.
>>
>>    Comment 1:  We must be barking up the wrong tree.  All the tests I
>> can recall doing in the past couple years have exonerated the T304.
>> Since the problem is manifest in the X-band system, and since the old
>> style X-band receivers did not show the compression, while the new style
>> ones do, is the problem somehow connected to the receivers, or the
>> switched power injection mechanism?
>
> One thought comes to mind.  If we have ruled out the downconverters,
> except for passive components, only the receiver and sampler are left
> in the X band system.  Are we seeing compression in the sampler module
> before the digitizer?  That can be tested by reducing the output power
> set point by 3 to 6 dB.  Our conventional set point produces a sampler
> RMS of about 11, so there is some room to reduce the power.  Have we
> already done this?
>